cloneElement passed into new MemberExpression fails with cryptic message

[Smolations]

CST version: 0.4.9

I am working on some angular generators, and my current work is around re-ordering an angular module definition. The goal is to keep the module definition as a clone so I don't have to rebuild from scratch (which I may have to try if all else fails) but, after cloning it, I am unable to add it to a new MemberExpression.

I wrote my own methods for inspecting the module tree so I could see the types of children contained in elements. First, I find the big CallExpression containing the definition. Below is what you see after calling .getSourceCode() on that expression:

angular.module('module.services', [
  ngDep,
])

  .service('svcOne', SvcOne)
  .service('svcTwo', SvcTwo)

Here is a small snippet of output as I inspected all of the children, so I could narrow down which element was the module definition (this is at the very end of the output since the module def is one of the last children):

-------------------------------------------------------
[Inspecting MemberExpression]:
angular.module('module.services', [
  ngDep,
])   [CallExpression]


     [Whitespace, Token]
.   [Punctuator, Token]
service   [Identifier]
-------------------------------------------------------

Once I reach that deep, I grab the CallExpression and save a clone. Then I try to create a new MemberExpression using the clone:

// i have verified that I am cloning the correct output by calling `.getSourceCode()` on it
const moduleDefCallExp = el.cloneElement();

// i created my own util service to help me, which is why i use `types.MemberExpression`
// to access the constructor
let growingMemberExpression = new types.MemberExpression([moduleDefCallExp]);

An error is triggered on that line, showing the following stack trace:

/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:37
            throw new Error(`Token expected but "${type}" found`);
                  ^
Error: Token expected but "undefined" found
    at ElementAssert.assertToken (/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:37:19)
    at ElementAssert.passToken (/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:214:9)
    at MemberExpression._acceptChildren (/home/vagrant/myproj/node_modules/cst/src/elements/types/MemberExpression.js:22:22)
    at MemberExpression._setChildren (/home/vagrant/myproj/node_modules/cst/src/elements/Element.js:638:14)
    at MemberExpression.Element (/home/vagrant/myproj/node_modules/cst/src/elements/Element.js:50:18)
    at MemberExpression.Node (/home/vagrant/myproj/node_modules/cst/src/elements/Node.js:11:33)
    at MemberExpression.Expression (/home/vagrant/myproj/node_modules/cst/src/elements/Expression.js:13:33)
    at new MemberExpression (/home/vagrant/myproj/node_modules/cst/src/elements/types/MemberExpression.js:4:29)
    at Object.formatNgModule (/home/vagrant/myproj/generator-component/lib/cst-util.es6.js:247:35)

Am I doing something wrong here? I followed the source code and it seems strange that a token error, or any other error for that matter, would be thrown given that I passed in a clone from an element that the parser itself created. Given the source (for ElementAssert) around the error...

    assertToken(tokenType, tokenValue)       {
        let {isToken, type, value} = this.currentElement || {};
 
        if (!isToken) {
            throw new Error(`Token expected but "${type}" found`);
        }
    // ...

...it seems that this.currentElement is not set, even though the constructor should call this._navigate(0) which sets that property:

    constructor(elements) {
        this._elements = elements;
 
        if (elements.length > 0) {
            this._navigate(0);
        }
    }

Thoughts?

[Smolations]

I also attempted to create an empty MemberExpression and then append the clone to it, but it appears that you cannot create an empty MemberExpression as I receive an error, both with
passing an empty array to the constructor:

/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:303
        while (this.currentElement.type === 'Punctuator' && this.currentElement.value === '(') {
               ^
TypeError: Cannot read property 'type' of undefined
    at ElementAssert._passExpressionInParens (/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:303:16)
    at ElementAssert.passExpressionOrSuper (/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:278:21)

...and when passing no arguments at all:

/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:37
            throw new Error(`Token expected but "${type}" found`);
                  ^
Error: Token expected but "undefined" found
    at ElementAssert.assertToken (/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:37:19)
    at ElementAssert.passToken (/home/vagrant/myproj/node_modules/cst/src/elements/ElementAssert.js:214:9)

[Smolations]

Doing more digging, when the MemberExpression is instantiated, super calls bubble up until Element's constructor eventually calls this._setChildren(children);, which eventually calls MemberExpression's override of this._acceptChildren(). Then, it appears that that override immediately will look for a token, which the CallExpression I passed is not:

  _acceptChildren(children) {
      // ...
      if (children.isToken('Punctuator', '.')) {
          // ...
      } else {
          children.passToken('Punctuator', '[');  // the error occurs here
          // ...
      }
      // ...
  }

So I'm wondering, how did the MemberExpression I inspected ever get a CallExpression as its first child?